[Webkit-unassigned] [Bug 241847] New: @supports selector fails for shadow dom elements

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=241847

            Bug ID: 241847
           Summary: @supports selector fails for shadow dom elements
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: j.nicklas at me.com

Created attachment 460411

  --> https://bugs.webkit.org/attachment.cgi?id=460411&action=review

Reproduction Example

The `@supports selector ()` fails for shadow DOM pseudo element tests.

An example for supported shadow DOM pseudo element styling is `input::placeholder { color: orchid }`.

Therefore the expected behaviour would be that `@supports selector(input::placeholder) {` matches.
Furthermore the expected behaviour would also be that `@supports not selector(input::placeholder) {` does NOT match.

Instead the current behaviour is that `@supports selector(input::placeholder) {` does NOT match.
In addition the current behaviour is also that `@supports not selector(input::placeholder) {` does match.

This behaviour can be reproduced on different Safari versions:

- iOS 15.5 Safari
- MacOS Safari Version 15.5 (17613.2.7.1.8) 
- MacOS Safari Technology Preview Release 146 (Safari 15.4, WebKit 17614.1.14.10.6)

Current Firefox and Chrome versions behave correctly.

Please see the attached reproduction example.

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